Integral scroll and gearbox for a compressor with speed change option

ABSTRACT

The volute is cast integrally with the gearbox base to allow closer radial tolerances to be used to improve efficiency. In the preferred embodiment, compressors for multi-stage compression are assembled with intercoolers and the integral volute is cast together with the impeller housing and the lower gearbox housing and the associated intercooler. Efficiency increases of 2% or more are achievable. In multistage applications, efficiency gains in the early stages are compounded in each subsequent stage. Speed changes that change center distance between bull gear and pinion are accommodated by an offset opening in the inlet and diffuser that can line up with the impeller shaft as well as an offset opening in the fluid seal despite a pinion gear change, by reorientation and remounting of those parts.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/921,547, entitled “Integral Scroll and Gearbox for a Compressorwith Speed Change Option”, filed on Apr. 3, 2007, which is hereinincorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to centrifugal compressors, suchas, for example, assemblies of compressors for multistage compressionwherein the integral casting further includes a gearbox and intercoolerhousings.

BACKGROUND OF THE INVENTION

Centrifugal compressors supply oil-free compressed gas in a variety ofindustrial applications. A common application of a centrifugalcompressor is in plant air systems, to supply a motive force for valveactuators and pneumatic cylinders used in robotic applications, as oneexample. Centrifugal compressors typically feature an impeller mountedin a closely-conforming impeller chamber. The chamber features an axialinlet port to allow fluid entry toward the center of the impeller. Fluidis drawn into the impeller due to its rotation at speeds that can exceed75,000 revolutions per minute (RPM). The rotation of the impellerpropels the fluid through an annular diffuser passageway and into asurrounding volute. The energy imparted into the fluid by the impeller'srotation increases the fluid's velocity and, consequently, pressure asthe fluid passes the diffuser passageway into the scroll or volute. Thediffuser passage way has inside and outside radial dimensions for eachcircumferential station of the impeller chamber and scroll. Bydefinition, the inside radius of the diffuser section corresponds to thedistance to the diffuser throat or the location at which the annularport or passageway has the smallest axial width for the given station,the diffuser section extending outwardly for the remainder of theannular passageway.

Traditionally, centrifugal compressors have featured a bolt onscroll/volute cover, which encompassed portions of the impeller chamber,the diffuser passageway and the volute-outlet passageway. U.S. Pat. No.4,181,466 is illustrative of a bolt-on component featuring a fluid entry51 and a volute 50 that is secured to the bearing housing 15 by aV-clamp 49. A difficulty with the bolt-on scroll/volute coverincorporating the volute is the effective control of tip clearancebetween the impeller and the inlet passageway and the clearance betweenthe impeller and the volute outlet. Due to the bolt-on constructionpreviously employed, machining costs and assembly costs affected thefinished cost of the product. The assembly of a plurality of componentsrequired the use of greater clearances around the impeller, whichsacrificed compressor efficiency. This, in turn, required larger driversand higher operating costs for electric power. Since each assembledcomponent has a manufacturing tolerance, the final clearance near theimpeller has to be sufficiently large to accommodate a situation whereall the tolerances in the individual components of the assembly turnedout within specification but all dimensions on the individual componentswere off from the ideal dimension and on the same side of the toleranceallowed.

Another problem with bolt-on volutes, i.e., 24 and 26, is the extraspace and mass taken up by that type of assembly. Such space couldbecome important in situations where ease of installation andmaintenance is important to serviceability. For example, as will beexplained below, use of bolt-on volutes (such as 24 and 26) hindersaccess to the driver shaft for an oil pump to be directly driven. Theextra housing thickness for each stage in a multi-stage skid couldpreclude a direct drive on the oil pump and may necessitate a separateelectrical drive for the oil pump. This would be undesirable in theevent of an electrical failure. In an electrical failure, the impellerbearings need lubrication, as the impeller slows from its operatingspeed of 75,000 RPM or more. Bearing failure could result with anelectrically driven oil pump if it stopped delivering oil too abruptlyon power failure. A power takeoff from the main drive shaft, which couldinvolve gears or belts, adds to the complication of packaged systems andtends to complicate access when maintenance is required.

One issue that remains unresolved by the integral casting of the voluteas part of the gearbox is what can be done if the end user needs acapacity change that involves a speed change to one or more stages in acompressor assembly. Normally, such a speed change involves a gear ratiochange. Typically, the end user prefers to simply change a pinion 34shown in FIG. 2 while retaining the much larger bull gear 32. Thereasons for this preference are cost and speed of getting thereplacement parts. It is far easier for the original equipmentmanufacturer to stock a variety of pinions than to have a lot of cashtied up in very large parts such as different bull gears 32. However,using a different sized pinion with the same bull gear changes thecenter to center distance between them and the scroll is integrally castto a fixed center to center distance.

SUMMARY

In accordance with certain embodiments, the volute is cast integrallywith the gearbox base to allow closer radial tolerances to be used toimprove efficiency. In one embodiment, compressors for multi-stagecompression are assembled with intercoolers and the integral volute iscast together with the impeller housing and the lower gearbox housingand the associated intercooler. Efficiency increases of 2% or more areachievable. In multistage applications, efficiency gains in the earlystages are compounded in each subsequent stage. Speed changes thatchange center distance between bull gear and pinion are accommodated byan offset opening in the inlet and diffuser that can line up with theimpeller shaft as well as an offset opening in the fluid seal despite apinion gear change, by reorientation and remounting of those partsincluding the bearings that support them. Either the pinion or the bullgear or both can be moved to change the shaft center distance toaccommodate the new gear pairing to get the desired speed.

The present invention, in the exemplary context of and integral scrolland gearbox, provides a way to accommodate the differing center tocenter distances of the gear drive from a speed change by allowing thescroll to accept an end plate with an eccentric opening that can bemounted in a variety of positions to accommodate different center tocenter distances for example. The bearing housing that is placed in thecasting at the gearbox location is selected to also accommodate thisoffset and an insert shown in FIGS. 7 and 8 can also be mounted tomaintain the relation of the inlet opening 76 to the position of theshaft 38 that supports the impeller 36 and the pinion gear 34.Alternatively, the present invention can accommodate changing the centerdistance between the bull gear and the pinion by moving the bull gearcenterline using offset bearing housings for its shaft, for example. Asyet another alternative and exemplary embodiment, the present invention,depending on the new desired speed, can have both shafts moved toincrease or decrease the center distance to accommodate the new gearingcombinations selected to get the desired speed.

These and other advantages of the present invention will become moreapparent to a person of skill in the art from a review of thedescription of the exemplary embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view a prior art of a three-stage centrifugalcompressor skid showing the first stage compressor housing with volutecast integrally with the lower gearbox housing and the first stageintercooler housing.

FIG. 2 is a section view along line 2-2 of FIG. 1.

FIG. 3 is a close up view of the first-stage volute-type scroll housingshown at the top of FIG. 2.

FIG. 4 is a close up view of a prior art bolt on volute-type scrollhousing typically used as an industry standard centrifugal compressor;

FIG. 5 shows an inlet assembly with the opening off center to address ashifted impeller shaft position from a change in pinion gear size on theimpeller shaft;

FIG. 6 is an end view showing the inlet of FIG. 5 assembled to a scroll:

FIG. 7 shows, the orientation of the inlet with the opening shiftedright;

FIG. 8 shows the orientation of the inlet with the opening shifted left;and

FIG. 9 is an exploded view showing how a change in pinion size can beaddressed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, this figure, which is in a perspective view, hasportions removed for clarity. For example, the motor driver for thepackage is omitted. The illustrated package comprises a first stage 10,a second stage 12, and a third stage 14. In essence, FIG. 1 is a drawingof a casting, which further comprises a first-stage intercooler housing16, a second-stage intercooler housing 18 and the lower end of thegearbox 20. An after-cooler (not shown) can be used after the thirdstage 14. The first stage 10 has an inlet 22 omitted from FIG. 1 butshown in section in FIG. 2. Second stage 12 has a differently configuredinlet section 24 as compared to the first stage inlet 22. Third stage 14has an inlet 26 similarly configured to inlet 24. The present invention,in certain instances, relates to the configuration of volute scroll 74and its complementary inlet 22. That configuration can also be used insecond stage 12 and third stage 14 within the scope of the invention.

The first stage 10 has been configured differently than stages 12 and 14to illustrate the difference between the prior-known technique(illustrated in stages 12 and 14) from the technique of the presentinvention exemplified in the first stage 10. It is also different thananother known technique as described in FIG. 4, item 90. It should benoted that the invention does not presuppose multiple stages and thedetails of the first stage 10 can be employed in a single stageinstallation or in a multi-stage installation, on one or more of thestages, all within the scope of the invention.

Referring again to FIG. 2, shaft 28 has a coupling 30 connected at itsend. The motor driver (not shown) is coupled to coupling 30. Shaft 28supports bull gear 32 in gear box 20. Pinion gear 34 meshes with gear 32to drive impeller 36 in first stage 10. Shaft 38 supports the impeller36 as well as pinion gear 34 and seals 40 along with bearings 42,disposed on either side of pinion gear 34. On the other side of the gearbox 20, another pinion gear 44 is supported on a shaft 46 to operateimpellers 48 and 50 on the second stage 12 and third stage 14 in tandem.Similar seal and bearing arrangements are used on shaft 46 as on shaft38. Mounted to the end of shaft 28 is an oil pump 52, directly connectedby a coupling 54.

As seen in FIGS. 1 and 2, the second and third stages, 12 and 14 aredifferent than the first stage 10. The housings 56 and 58 arecylindrically shaped and receive a combination inlet/volute 24 and 26respectively. Bolts 64 and 66, respectively secure the combinationinlet/volute respectively to housings 56 and 58. The housings 56 and 58are cast integrally with the lower gear box 20 and the intercoolerhousings 16 and 18. Second and third stages 12 and 14 illustrate theprior known technique and are included in the illustrated three-stagesystem to provide contrast for a clearer understanding of the advantagesof the present invention. FIG. 4 also illustrates a prior art technique,which provides further contrast and understanding of the advantages ofthe present invention. In the illustrative stage 90 of FIG. 4, themachined scroll/volute 90 is a complicated piece having numerousmachined surfaces, each of which necessarily has a tolerance on one orboth sides of the ideal dimension. Impeller 92 has a plurality of blades96 extending radially from near its center. A clearance in the radialdirection is required as between the blades 96 and surface 98 oninlet/volute 94. The location and orientation of this clearance is alsoseen in FIG. 3, which is a close-up of first stage 10, illustrating theclearance in the case of the present invention. The clearance 72 in thefirst stage 10 can be reduced to less than 0.020 inches as compared tothe stage 90 where the counterpart clearance can run in the range of0.024-0.035 inches or greater. The clearance 72 is obtained solely as aresult of a casting followed by a machining process. To date,commercially available equipment of the type shown in FIG. 4 has notbeen built with smaller clearances. While, theoretically, a coatingprocess can be employed to further reduce clearances in the prior FIG. 4design below 0.024 inches, practically, these techniques have not beenemployed in centrifugal compressor applications for reasons of qualitycontrol problems and prohibitive cost.

The reason a smaller clearance is obtained in the first stage 10 is thatit incorporates a volute type scroll as the housing 74. Inlet 22 has anopening 76 made of a surface 78, which conforms to the outer peripheryof blades 80. The radial clearance 72 eventually becomes an axialclearance in conformity to the shape of blades 80. Since the volute iscast integrally to the housing 74 there are fewer surfaces to machine onthe casting and on inlet 22 to fit them up. The ultimate blade clearance72 can be smaller than in the stage 90 because there are feweropportunities for the accumulated tolerances on the various machinedsurfaces to add up when the volute type scroll is cast integrally ashousing 74. There are also reduced man-hours for assembly of the firststage 10 as well as labor savings in reduced machining. The disadvantageof the second stage 12 is that by combining the volute into the inlet 60and then inserting the inlet 60 into the cylindrically shaped housing 56the outer profile of housing 56 is increased due to a near doubling ofthe wall thickness at the periphery. To illustrate the concept, had thefirst stage 10 been built in the same manner as the second stage 12using the same exterior dimensions for the casting shown in FIG. 1,there would have been no room to mount the oil pump 52 and coupling 54to the shaft 28 between the first and second stages 10 and 12respectively. As previously stated, being able to power the oil pump 52off of shaft 28 becomes an issue if there is a power failure from theperspective of protecting the bearings such as 42. The other alternativeof simply making the entire casting larger adds significant cost to thefinished product.

It should be noted that with regard to the first stage 10, that thediffuser plate 82 is secured to inlet 22 with bolts 84 before fitting upinlet 22 to the volute type scroll housing 74 using bolts 86. Theclearance 72 minimization allows the first stage to achieve anefficiency improvement of 1-2% and slightly more. This improvement ismagnified in the subsequent stages of compression. Operating expensescan be reduced and a smaller driver utilized because of the reduction ininternal leakage from use of smaller clearances. Of course, even greaterefficiency can be obtained from using the volute type scroll castintegrally as the housing in all stages in a multi-stage assembly suchas shown in FIG. 1. The oil pump 52, even if there is a power failure,continues to deliver enough oil to all the bearings as shaft 28 slowsdown but continues to drive the oil pump 52.

Referring to FIG. 2 it can be seen that gearbox 20 is made integrallywith housing 74 to accept a predetermined spacing between shaft 28 forbull gear 32 and shaft 38 for the pinion gear 34. To make all the partsgo together, the air seal 40 has a properly located bore (not shown)through which the pinion shaft 38 extends. The inlet assembly 22 has aninlet opening 76 to align it with the impeller 36. Referring to FIG. 3,it can be seen that the diffuser 82 is part of the inlet assembly 22 andalso features an opening (not shown) in which the impeller 36 resides.

The question comes up and the present invention addresses, what happensif a compressor assembly is constructed to a given speed for the firststage 10 for example and the operator has experienced a change inconditions and want to increase the speed. The original equipmentmanufacturer wants to be able to help the customer change the speed butissues arise as to what to stock in inventory and the cost ofmaintaining a variety of parts to accommodate a variety of selecteddriven speeds. Typically, the bull gear 32 is the largest gear in thegearbox and is very expensive to produce in a variety of teeth countconfigurations. If the bull gear 32 is not changed then a speed changeinvolves changing the teeth count of the pinion 34 to reduce teeth for aspeedup or increase teeth for a slowing down of the first stage 10 forexample. However, fitting a new pinion gear 34 changes the center tocenter distance between shafts 28 and 38 and the integral casting of thegearbox 20 and the housing 74 was to a fixed center to center distance.

It is believed the present invention solves this problem. If the pinion34 is replaced with a smaller gear to speed up the first stage 10, forexample, the bearings 42′ on either side of new pinion 34′ must berelocated within the housing 20 to adapt to the new center to centershaft distance. FIG. 9 shows the bearing housings 43 with offset bores45 to offset the bearings 42′ for a change in shaft center distancecreated by use of the new pinion 34′. In order to allow the shaft 38′ toenter the housing 74 through the air seal 40 the opening in it 47 ismade eccentric to its center. This eccentric bore concept for the sealis also addressed for the inlet assembly 22′ and the diffuser 82′connected to it. FIGS. 5-8 show the inlet assembly 22′ with anoff-center opening 76′ relative to the bolt circle diameter that acceptsbolts 86 (see FIG. 3). FIG. 6 shows the modified inlet assembly 22′mounted to housing 74 of the first stage, for example. FIGS. 7 and 8show the rotated left and rotated right positions for the inlet 76′,respectively. Those skilled in the art will appreciate that the opening49 in the diffuser 82 is preferably aligned with opening 76′ in inlet22′ so that the impeller 36 fits within diffuser 82 while the shaft 38′goes through an eccentric opening relative to the center of seal 40 sothat seal 40 fits in the same opening as before but now creates anoffset bore for shaft 38. The same result occurs for the bearings forshaft 38′. As a result of the offset opening 76′ in inlet assembly 22′and the matching opening in the diffuser 82′ attached to it as well as asimilar offset in air seal 40 there are now two positions at minimum forthe center to center distance between shafts 28 and 38′ if they are keptat the same horizontal plane. Even more center to center distancechanges are possible if the shafts are not limited to being in the samehorizontal plane. Alternatively, the end user that requires a speedchange can also buy a different inlet assembly 22′ with a diffuser 82having a matching bore offset to accommodate the impeller 38 and justpurchase those components with a new air seal 40 and relocate thebearings 42 closer or further away, as needed and everything can go backtogether and function in the existing equipment that has the integralgear box 74 and housing 74.

As an alternative, offset bearing holders similar to those shown for thepinion shaft 38′ can be used for the bull gear shaft 28. In that way,the bull gear can be relocated closer or further from a pinion shaft 38that itself can be moved or left where it is. In a given gearbox andscroll combination housing the speed can be changed with a change of thepinion size, the bull gear size or by changing both depending on thedesired end speed for the compressor stage that is desired. The centerdistance can be increased or decreased by moving one or both pinion andbull gear shafts. Offset mounting for the shafts are made possible bymounts with eccentric capabilities that allow the original componentssuch as bearings and seals to be mounted in a variety of positions toaccommodate the new shaft location within an existing gearbox. Speedchanges are now possible for such precast units without major expense ofobtaining new gearbox with scroll integrated housings.

While the invention has been described and illustrated in detail in thedrawings and foregoing description, the same is to be considered asillustrative and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the scope of the claims beloware the full scope of the invention being protected.

1. A compressor, comprising: an integrally produced combination of a atleast a portion of a gearbox housing and at least a portion of acompressor housing with openings at a predetermined distance for adriving shaft into the gearbox housing and a driven shaft from thegearbox housing into the compressor housing; the compressor housingfurther comprising a seal assembly through which a driven shaft enters,the driven shaft further comprising a first driven gear and an endelement disposed on the driven shaft and located in the compressorhousing; the gear box housing further comprising a driving shaft and adriving gear engaged to the first driven gear; the seal assembly furthercomprising an offset opening with respect to a center thereof, whereuponthe first driven gear is replaceable with a second driven gear of adifferent size that changes the shaft to shaft center distance and theseal assembly can accommodate the changed shaft to shaft center distanceby reorientation of the offset opening.
 2. The assembly of claim 1,further comprising: an inlet assembly further comprising an inletopening located off center thereto, the assembly adapted to be mountedto the compressor housing in a plurality of orientations to change theposition of the inlet opening with respect to the compressor housing. 3.The assembly of claim 2, wherein: the inlet assembly is mounted to thecompressor housing on a side opposite from the seal assembly.
 4. Theassembly of claim 3, wherein: the inlet opening and the offset openingin the seal assembly can be aligned in more than one position withrespect to the compressor housing.
 5. The assembly of claim 4, wherein:the inlet and offset openings are aligned in the same plane as theshafts.
 6. The assembly of claim 4, wherein: the inlet and offsetopenings are above or below a plane that intersects the shafts.
 7. Theassembly of claim 2, further comprising: a diffuser comprising adiffuser opening and supported by the inlet assembly; the diffuseropening aligned with the inlet opening such that both the openings movea like amount on reorientation of the inlet assembly with respect to thecompressor housing.
 8. The assembly of claim 7, wherein: the offsetopening is capable of being aligned with the diffuser and inlet openingsin a plurality of orientations with respect to the compressor housing;the offset, diffuser and inlet openings are capable of alignment in aplane defined by the shafts or above or below the plane; and the endelement comprises an impeller and the compressor housing comprises atleast a single stage centrifugal compressor.
 9. (canceled) 10.(canceled)
 11. A compressor, comprising: an integrally producedcombination of a at least a portion of a gearbox housing and at least aportion of a compressor housing with openings at a predetermineddistance for a driving shaft into the gearbox housing and a driven shaftfrom the gearbox housing into the compressor housing; the compressorhousing further comprising a seal assembly through which a driven shaftenters, the driven shaft further comprising a first driven gear and anend element disposed on the driven shaft and located in the housing; thegear box housing further comprising a driving shaft and a driving gearengaged to the first driven gear; an inlet assembly further comprisingan inlet opening located off center thereto, the assembly adapted to bemounted to the compressor housing in a plurality of orientations tochange the position of the inlet opening with respect to the compressorhousing.
 12. The assembly of claim 11, wherein: a diffuser comprising adiffuser opening and supported by the inlet assembly; the diffuseropening aligned with the inlet opening such that both the openings movea like amount on reorientation of the inlet assembly with respect to thecompressor housing.
 13. The assembly of claim 12, wherein: the diffuserand inlet openings are capable of alignment in a plane defined by theshafts or above or below the plane.
 14. The assembly of claim 13,wherein: the seal assembly further comprising an offset opening withrespect to a center thereof, whereupon the first driven gear isreplaceable with a second driven gear of a different size that changesthe shaft to shaft center distance and the seal assembly can accommodatethe changed shaft to shaft center distance by reorientation of theoffset opening.
 15. The assembly of claim 14, wherein: the inletassembly is mounted to the compressor housing on a side opposite fromthe seal assembly.
 16. The assembly of claim 15, wherein: the inletopening and the offset opening in the seal assembly can be aligned inmore than one position with respect to the compressor housing.
 17. Theassembly of claim 16, wherein: the offset opening is capable of beingaligned with the diffuser and inlet openings in a plurality oforientations with respect to the compressor housing.
 18. The assembly ofclaim 17, wherein: the offset, diffuser and inlet openings are capableof alignment in a plane defined by the shafts or above or below theplane.
 19. The assembly of claim 18 wherein: the end element comprisesan impeller and the compressor housing comprises at least a single stagecentrifugal compressor.
 20. A compressor, comprising: an integrallyproduced combination of a at least a portion of a gearbox housing and atleast a portion of a compressor housing with openings at a predetermineddistance for a driving shaft into the gearbox housing and a driven shaftfrom the gearbox housing into the compressor housing; the compressorhousing further comprising a seal assembly through which a driven shaftenters, the driven shaft further comprising a first driven gear and anend element disposed on the driven shaft and located in the compressorhousing; the gear box housing further comprising a driving shaft and adriving gear engaged to the first driven gear; the driving shaftcomprising bearings with off-center mounts to allow the driving shaft tobe moved closer or further from the driven shaft to accommodate a changein at least one of the gears.
 21. The assembly of claim 20, wherein: theseal assembly further comprising an offset opening with respect to acenter thereof, whereupon the first driven gear is replaceable with asecond driven gear of a different size that changes the shaft to shaftcenter distance and the seal assembly can accommodate the changed shaftto shaft center distance by reorientation of the offset opening.
 22. Theassembly of claim 20, wherein: the driven shaft comprises a bearingassembly having bearings movable within an offset mount that allows thedriven shaft to be moved closer or further from the driving shaft byreorientation of the bearings in their mount.